The maxim nemo iudex in sua causa (1)--no man should be judge in his own case--is widely thought to capture a bedrock principle of natural justice and constitutionalism. The U.S. Supreme Court calls it "a mainstay of our system of government" (2) and regularly invokes it in diverse contexts (3)--most famously as a principle of natural law in Calder v. Bull (4) and, implicitly, to justify constitutional judicial review in Marbury v. Madison. (5) The maxim has venerable roots in the common law, the leading precedent being Bonham's Case. (6) And it rests upon a principle of impartial decisionmaking that has undoubted appeal, both on deontological and consequentialist grounds. (7) As we will see, the appeal of impartiality is so strong that legal and political actors and commentators have extended the scope of nemo iudex well beyond judging in the strict sense, to cover decisions by many types of officials in many institutions.

Despite all this, I will argue that the nemo iudex principle is an exaggerated and misleading half-truth. Sometimes rulemakers in public law do and should design institutions with a view to the nemo iudex principle. In other cases, however, they do not and should not. In many settings, public law makes officials or institutions the judges of their own prerogatives, power, or legal authority. Officials or institutions may determine their own membership, award their own compensation, rule on the limits of their own jurisdiction, or adjudicate and punish violations of rules they themselves have created. Some examples:

* In many jurisdictions, legislators determine the boundaries of the districts from which the legislators themselves are elected, or otherwise structure the system by which they are elected. (8)

* In many jurisdictions, legislatures have broad authority to determine the qualifications of their own members and to expel members. (9)

* In many jurisdictions, legislators set their own salaries and compensation. (10)

* The President arguably has the power to pardon himself and clearly has the power to pardon his friends, family, and advisers. (11)

* The Vice President arguably has the power to preside at his own impeachment trial and clearly has the power to preside at the impeachment trial of friends and political allies. (12)

* A ubiquitous feature of the administrative state is that agencies combine the functions of rulemaking, prosecution, and adjudication. (13)

* In America, federal judges and many state judges rule on the constitutionality of legislative acts setting judicial salaries. (14)

* In many jurisdictions, judges have the final say over the limits of judges' power, prerogatives, and jurisdiction. (15)

* A federal judge may rule on her own immunity from suit, (16) rule on motions asking her to recuse herself for bias, and decide whether to hold litigants in contempt for violations of her own commands. At the level of the Supreme Court, each Justice rules on motions asking that Justice to recuse himself, and the rulings are unreviewable. (17)

The list is heterogeneous on several dimensions, which I will explore at length below, but that very heterogeneity illustrates that the nemo iudex principle is qualified in many settings and on many different grounds.

In this Essay, I will offer two claims, one destructive and one constructive. The destructive claim is that the nemo iudex principle cannot even be understood as a presumption to which public law sometimes makes exceptions; rather, it amounts to little more than a banal counsel that impartiality is sometimes an important value in institutional design. Impartiality constantly trades off against and competes with other values. Far from being a mainstay of our system of government, the most that can be said is that the nemo iudex principle sometimes holds and sometimes does not.

As for the constructive claim, I will attempt to identify the main grounds on which, and the main conditions under which, rule designers depart from, override, or qualify the nemo iudex principle. As we will see, in some cases there is no impartial official or institution in the picture, so that wherever decisionmaking authority is lodged, someone or other will have to be the judge in his own case. In other situations, even where it would be feasible to respect the nemo iudex principle, the costs of doing so will exceed the benefits. In general, this will be the case when and because impartiality trades off against one of several competing considerations: the benefits of expertise, the value of institutional autonomy and independence, or the motivation and activity level of officials or institutions.

The upshot is that it is never sufficient to argue that a proposed institution, or a proposed interpretation of ambiguous constitutional rules or practices, would violate the nemo iudex principle or would "put the fox in charge of the henhouse." One must go on to ask whether the conflict is avoidable or unavoidable--and, if it is avoidable, whether it would be good or bad overall to avoid it. As we shall see, in a range of cases, violations of nemo iudex are either unavoidable or affirmatively desirable, on balance.

The largest aim is to illustrate a general point about how constitutional and institutional designers manage political risks. Among the various risks that rule designers in public law must consider is the risk of self-dealing or self-serving bias on the part of decisionmaking officials or institutions. Yet there are many countervailing risks to consider, which implies that rule designers will have to trade off those risks against one another: rather than selecting maximal precautions against official or institutional self-dealing, they will have to select optimal precautions. (18) In the most difficult cases, the nemo iudex principle appears on both sides of the balance, so that preventing self-dealing by one decisionmaker will increase the risks of self-dealing by another decisionmaker. In such cases, the principle is in conflict with itself, and an appeal to it will necessarily be question begging. A well-rounded analysis will consider risks of bias that may arise on all sides of the relevant institutional questions.

Part I examines several versions of the nemo iudex principle and addresses its scope and weight. Part II examines cases in which a violation of nemo iudex is unavoidable wherever decisionmaldng authority is lodged, so that the principle is in conflict with itself. Part III examines cases in which the value of impartial decisionmaking embodied in nemo iudex trades off against other values: the direct costs of appointing an impartial decisionmaker (Section III.A), expertise and information (Section III.B), institutional autonomy and independence (Section III.C), or institutional "energy" and activity levels (Section III.D). Part IV offers some rules of thumb for identifying conditions under which rule designers should or should not entrust officials or institutions with the authority to act as judges in their own cause. A brief Conclusion follows.

NEMO IUDEX AND CLOSE RELATIVES

Although I will speak throughout of the "nemo iudex principle," this is actually a simplification for ease of exposition. In fact there are multiple Latin tags whose content is more or less equivalent. These include nemo debet esse iudex in propria causa (no one ought to be judge in his own cause) and nemo potest esse simul actor et iudex (no one can be both litigant and judge at the same time); (19) the latter version clarifies that the principle forbids simultaneous judging and litigating in the same case.

Core and Periphery

If there is an inviolable core to these maxims--and I will later suggest that there is not--the core is that no person should be permitted to judge his own cause by sitting as a judge over litigation to which he is a named party. There are, however, a variety of ways of extending nemo iudex outward from this situation. For one thing, the principle is often said to apply when a judge sits to decide a case in which he has a more or less direct financial interest, even if the judge himself is not also one of the nominal litigants. (20) A slight further extension involves cases in which the judge's relatives or friends have a financial interest. Still further out are scenarios in which the judge's interest in the case might expand the power or perquisites of the judicial branch as a whole, in which the judge holds only a fractional share, (21) or of the government as a whole, in which the judge's fractional share is smaller still. Finally, the most aggressive extensions posit that not merely an interest in the litigation, but an appearance of an interest, such that the judge's impartiality "might reasonably be questioned," (22) suffices to trigger the principle.

Moreover, although the principle and its relatives speak of judging, they have long since been extended to embrace other types of decisionmaking that are implicitly analogized to judging...